This invention relates to an acoustic system and method for performing operations, such as flow testing, in an oil or gas well. These operations are performed using a plurality of downhole devices controlled by one or more controllers responsive to one or more acoustic receivers.
After an oil or gas well has been drilled, a drill stem test is typically performed to check the pressure in the well under flow and shut-in conditions. This provides information relevant to deciding whether to complete the well for producing oil or gas from one or more formations intersected by the well. A similar production test is sometimes performed on a well that has been completed and put on production.
A formation tester valve and a circulating valve are devices typically used to conduct a drill stem or production test. The tester valve is repeatedly opened and closed to allow and prevent oil or gas flow from the well so that the pressure in the well can be checked under such flow and shut-in conditions. A downhole recorder or gauge can record the data for transmission to or retrieval at the surface. After the desired cycling of the tester valve has been completed, the circulating valve is opened to allow fluid to be circulated between the surface and downhole.
Typically these valves do not need to be operated until they are at a desired depth in the well. Thus, there is the need for some way to operate the valves when they are down in the well. Although the valves can be automatically controlled such as by a downhole microprocessor-based controller so that they perform desired operations at predetermined times, tester and circulating valves typically need to perform their functions at times that cannot be predetermined. In this case, there needs to be some way of communicating from the surface a command signal that will initiate or otherwise affect operation of the valves positioned downhole.
This need for surface to downhole communication has been well recognized in the oil and gas industry, and many techniques have been proposed. For example, a flow testing apparatus can be lowered into a well on an electrically conductive cable, known as a wireline, so that electrical signals can be transferred between the surface and the apparatus down in the well. As another example, the flow testing apparatus can be lowered into a well as part of a pipe string which can be mechanically manipulated (reciprocated or rotated) to operate the valves. As a further example, pressure signals can be sent through fluid in the pipe string or in an annulus around the pipe string.
These prior techniques have shortcomings. For example, the wireline and pipe string manipulation techniques call for special sealing requirements at the mouth of the well where the movable wireline or pipe string passes into the well, and the pressure signaling technique requires carefully controlled pump operation at the surface and exerts additional pressure on the downhole environment. These shortcomings are especially significant in a subsea well where the mouth of the well is on the ocean floor. Using mechanical manipulation, it also is difficult to determine how much weight is being applied to obtain the desired mechanical response. In pressure signaling, the condition of the well fluid providing the transmission medium is important because if it degrades, the pressure signals applied at the mouth of the well will be weak, obscure or non-existent downhole where the pressureresponsive receiver is. All of these techniques require a significant surface disturbance, which decreases the safety of the overall operation.
Because of at least these shortcomings of the aforementioned previously proposed flow testing systems and methods, there is the need for an improved system and method that does not have these shortcomings. As more fully disclosed hereinbelow, such an improved system and method should use acoustic technology. Such an improved system and method should allow for multiple downhole apparatus to be selectively controlled via acoustic control signals sent from the surface or from one downhole apparatus to another.